My research and experience:
https://www.rcgroups.com/forums/showthread.php?2475611-Evolution-of-an-RC-enthusiast-in-search-of-reliability-ZMR-250-X8-Coaxial#post32362210
Roberts presentation at Dronecon:
https://www.youtube.com/watch?v=HywcbNHroQg
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This is all excellent stuff.
I bought the D800 for a steal as a scratch and dent from HK (photographed for the webite and reboxed ).It’s been stuck in a case since as the hexacopters get finished off (ish).It will be fun to get it out and give it a go.Not quite the sky crane I once imagined it to be it will still have a bit of grunt to spare.Maybe I can use it for mowing the lawn.
My Setup in X8 would be :
Top U8-135 Kv motor with CF 29x9.5 prop
Bottom U8-170 Kv motor with CF 28x9.2 prop.
I would appreciate comments about this Setup.
So does Ardupilot not offer a way to blend the motors? I have castle creation escs and the new firmware has an adjustment to set for more efficiency or more performance on an esc. I wonder if setting my lowers to more performance and leaving the tops on medium or efficient would be the same as blending so the bottom motors would work as hard as the top
The old U8 don’t work well at 6s and 28’’ at 8s are a little bit bigger for me
Theoretically you would want the faster higher pitch on the bottom but you may not be able to find the opposite 29x9.2 on top 28x9.5 on bottom. The bottom needs to go faster and you can do that multiple ways. So you don’t have to have higher kv and higher pitch.
I am on a similar project, and first thing was go to ecalc and try some configurations to find weight and others parameters, I think most important is battery voltage, for U8, 6-12s and flight duration in amps.
Seeing old u8 chart (new series are here) and some imputs, the main problem with large props (and heavy) are lazy behaviour and windy conditions, this means forget 6S, so go to 8-10S and this means forget 29-30 props. 28-24" propellers is the max diameter for my understanding, choice by voltage 8-10S and kv motor.
So kv100 and 10S 28-26 prop, kv135 and 8s 28-26 prop, and kv170 8s 26-24 prop I guess will fine.
About top-bottom configuration, I read a lot and seems with large props and low rpm in a efficiency config affects less the effect on bottom motors but whatever cofiguration, the bottom motors are gonna eat more power, so focus in good motor-prop in charts. Last thought is with same prop-motor combination, you can rotate motors bottom-top for compensate the extra work.
I’m waiting for some test of the new 190kv at 6s, perhaps can work… the problem at 8-10s are the batteries, the standard for big copters are the 6-12s
Interesting test https://www.youtube.com/watch?v=Mt0owkbw2jk
If you contact them they build what you want…http://www.gensace.de, well, you should buy some units I guess
I fly octo quad for safety reason (even real size one are build that way.You lose a bit of efficiency but with 8 motors / ESC you gain safety. Same size props up and down (18 x 5.5 CF T-Motor kind). Here is a full size one:
I see that thrust tuning of upper VS lower props was mentioned in this thread, but is there a practical way to do it in arducopter? I ask because I am planning to split power between upper and lower prop sets and would like to tune so batteries are consumed roughly equally.
This video from stratus production is biased negatively against X8 frames as it takes only one parameter into account. For example the extra weight required for an octo versus a lighter and compact X8 is not taken into account.
I believe the efficiency loss of a coax config versus a flat octo config is much less than said in the mentioned video , taking everything into account, and is much more wind resistant and compact.
Mike what do you think about setting the ESC to be more aggressive on the bottom than top?
as you can with the castle creations v5 Escs that allow you to set for longer flight or more responsive higher performance
Depends on what that does exactly but what you want in the end is for the bottom props to spin faster since they live in faster moving air than the top props.
Building an X8 is truly a black art. No two X8’s are going to be the same because getting matching components is hard. You might find that at 16" you can easily get a 15" prop for the bottom but in another size you can’t find a slghtly smaller or larger prop. Same with motors in some vendors and sizes you can find a 700kv and 780kv for the same motor but in other sizes you have huge jumps.
So it is very much a design that begs for experimentation and tuning/tweaking.
BTW I love eCalc and use it all the time for what-if comparisons but eCalc just does not have the variable options to do X8 estimates accurately.
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Hi I know this is an old thread, but given that ecalchs suggest either a 1" larger bottom prop or a prop with a higher pitch on the bottom, as stated in this post it is difficult to find this combination. I am currently using 12 1/2" KDE on top and bottom…
My question is does anyone see a problem with using a tri- prop KDE 12 1/2" tri prop on the bottom?
My question is does anyone see a problem with using a tri- prop KDE 12 1/2" tri prop on the bottom?
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Hi
In my case I use same 380kv motors for top and bottom.
Initially I used 16x5.5 for top and 15x5.5 for the bottom ones. I noticed that the top were getting really hot.
I tried replacing the top props with 15x5.5 and what do you know, I got better stability and even power consumption is lower.
GL
Thanks Gal
The current config I have is similar to yours with both top and bottom the same prop, it flies well. I would like to optimize the bottom motors as they do not work as hard as the top, I will run some tests as I described with duel props top and tri props bottom, I have some spare motors and KDE hubs both duel and tri, and also enough props - I will rig up a drone arm and run some test with both duel and the change the bottom to tri blade… The thrust can then be measured with a scale on the opposite end of the prop arm ~ thanks
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3 blade props are less efficient that 2 blade props, so that alone will make your lower motors work harder and seem like their output is more balanced - in reality if a top motor fails the bottom motor with 3 blade prop will have to work super-hard to cope.
From what I understand, many have tried to use different sized motors and props for bottom and top motors in the X8/Octaquad configuration, and it probably works more by luck than by design.
I think you are better off using all the same motors and props for reliability and spare parts if nothing else. Arducopter will know what to do and balance their output as required.
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Well, checking new ways to improve things and learn new things is at least for me as a hobbyist a way of life, though I do agree with @xfacta on this issue. I initially used different motors on top as well and didn’t get stabilized quad.
Anyway here is something to make you smile.
GL with the tests and if you find something interesting do share.
Gal
@xfacta
I questioned this , as each esc is connected to the cube , does the cube compensate the top/ bottom motor speed on each arm? Or is the output more linear, sending the same power to both motors? Looking at the logs it appears the bottom motor doesn’t work as hard. As for tor tri props, I know the motor works harder, but it also provides more lift, as I have a similar quad using tri props to carry a slightly heavier camera. Thanks Shawn